1. Field of the Invention
This invention relates to a fuel system for an internal combustion engine operated with fuel gas. The fuel system has an evaporator in which the fuel, which is stored in the liquid state, is transformed by the application of heat into a gaseous state. The evaporator has a first heating device for the fuel gas, by means of which a portion of the waste heat of the internal combustion engine can be transmitted to the fuel gas that is in the evaporator.
2. Technical Considerations
Internal combustion engines powered by fuel gas are frequently used in industrial trucks, such as fork-lift trucks, as well as in passenger vehicles. The fuel gas most commonly used for this application is conventionally termed “LPG” (liquid petroleum gas) and consists primarily of propane and/or butane.
The fuel system of a conventional internal combustion engine typically has an evaporator in which the fuel gas, which is stored in the liquid state, is transformed into a gaseous state by applying thermal energy to the fuel gas. This addition of thermal energy generally takes place using the heat from the coolant of the internal combustion engine, which can be used to heat a housing of the evaporator. The evaporator thereby also acts as a pressure regulator so that the fuel gas is available at the output of the evaporator in a gaseous state and at a defined pressure. An additional component of the fuel system, located downstream of the evaporator, is either a mixer, the function of which corresponds to a carburetor in a gasoline-powered engine, or an injection system.
For safety reasons, it is important that under all operating conditions only gaseous fuel gas is in the parts of the fuel system that are located downstream of the evaporator. One particularly hazardous operating condition is the starting of an internal combustion engine in a cold environment when the coolant fluid of the internal combustion engine has not yet been heated. Under such operating conditions, the accumulation of liquid fuel gas in the injection system and in the lines leading to it initially leads to an over-enriched air-fuel mixture in the internal combustion engine, which, therefore, does not start. Consequently, additional liquid fuel gas accumulates behind the evaporator, which ultimately causes a significant safety problem.
Therefore, it is an object of the invention to provide a fuel system for a fuel gas engine which safely prevents an accumulation of liquid fuel gas behind the evaporator.